This invention relates to the field of multiple layer plastic extrusion, and more particularly to assemblies in which multiple thin or micro-layers of polymer material are formed which polymer material may be from two or more individual extruders, and delivered to a multilayer combining adapter in association with an extruder die or other utilizations operated.
Flow dividers for dividing one or more plastic polymer flows, such as from a plug type multi-layer adapter, have been employed in the co-extrusion of multi-layer films. The primary principle in the use of a flow divider includes the formation of a relatively large number of discrete polymer flow segments or layers that are then combined to form a layered structure that exhibits more uniform individual flow velocity profiles between layers.
In conventional apparatus, distortion of the layers can occur due to the rheology of the polymer material and the geometry of the flow passages. Further, in many such installations and equipment, it is necessary to place the flow divider and flow combining apparatus substantially upstream or a substantial distance from the distribution channel or manifold of the extrusion die. While some of these problems can be reduced by placing the layering and combining adapter closer to the die manifold or even in the die itself inherently, the structure of the equipment used has caused differential flow rates to occur at the combining point or region, and has caused other lack of uniformities so as to impair the quality of the multi-layer film product.
A further drawback of prior art designs resides in a difficulty of maintaining very thin skin layers. Layer uniformity with poor accuracy limits the ability to extrude thin layers of polymers with improved properties that can yield significant cost savings. Further difficulties with many of the flow dividers are the fact that they are complicated and expensive, and lack an ability to provide individual selection of flow paths and flow path areas or thicknesses without changing out and replacing an entire flow dividing block.
A need exists for an improved feed block employing a multiple layer flow combining adapter that provides more precise control of individual segments of the output from an extruder to be combined with similar outputs from one or more additional extruders in such a manner that the layer uniformity may be accurately retained, and thinner layers may be made with greater reliability.